Science fiction is one of those funny things that follows the same logic as the Supreme Court's stance on pornography: you may not be able to come up with a perfect definition that fits all the cases, but you know it when you see it. It's a genre that easily subsumes other genres. You can shoe horn mystery, horror, adventure, romance, or any other genre into a science fiction mold. The result? It's almost invariably shelved under science fiction. You ever see Asimov's robot mysteries filed next to Sandra Brown? Science Fiction is the barbeque of genres. Take any cuisine of food, and the instant you're cooking on a grill, it's barbeque. Same thing, take any story and the instant you add the dash of science fiction and you leave the other genres behind.

Take something like Neal Stephenson's Baroque Cycle. It's historical fiction dealing with the creation of the modern concept of currency and wrapped around the development of modern conceptions of science. It's got one science fiction element in the form of a deus ex machina of a resurrection potion, but nothing else about the story in particular or in general would suggest that it is science fiction. And yet the trilogy inarguably fits within science fiction to those who have read it. The trappings we associate with science fiction, the death rays, aliens and starships, are incidental to what makes a tale science fiction at its heart. Science fiction is a particular way of thinking, a rapt desire to figure out how and why things work. It's aimed at the notion of the universe being knowable. So it's no surprise in that light that many science fiction stories are futuristic, that the speculation of how the universe works often leads to the counterfactual.

Leonard Nimoy fought for years against the obsessive association of himself with the character from a three season failed television series, going so far as to pen a book entitled I Am Not Spock. But in an interview once he told how it wasn't until the nineties that he really got deep down why it was that "Star Trek" had mattered so much. His cell phone rang, and he flipped it open to answer and realized that here he was, thirty years later, with an exact working model of the cardboard communicators he'd spent the sixties flipping open on camera. Science fiction is the art in which our right brains doodle visions of the future. What was imagined can be eventually built. And science fiction spends its volumes working out the implications and moral calculus of those developments decades before their inner workings are sketched by an engineer's stylus.

This is not simply an exercise in speculating on things that future science will figure out, that would grow tedious quite quickly. Science fiction also serves as a thinking exercise, offering the thought experiments of potential developments as a way of understanding the world in which we already live. Science fiction is a tool of the societal right brain, asking "what if?" in order to cast "what is?" into a knowable perspective.

That's not to say there's not a lot of execrable science fiction out there that plays as little a role in right brain meditation as huffing paint, but then to paraphrase Sturgeon, ninety percent of everything is crap, so we shouldn't worry too much about ninety percent of science fiction that can be flushed.

Steven Lloyd Wilson is the sci-fi and history editor. You can email him here or follow him on Twitter.